Use inform to send websocket upgrades instead of a regular sending

lib/bandit/adapter.ex

@@ -214,6 +214,8 @@ defmodule Bandit.Adapter do
     if get_http_protocol(adapter) == :"HTTP/1.0" do
       {:error, :not_supported}
     else
+      # inform/3 is unique in that headers comes in as a keyword list
+      headers = Enum.map(headers, fn {header, value} -> {to_string(header), value} end)
       {:ok, send_headers(adapter, status, headers, :inform)}
     end
   end

lib/bandit/websocket/handshake.ex

@@ -69,19 +69,21 @@ defmodule Bandit.WebSocket.Handshake do
     hashed_key = :crypto.hash(:sha, concatenated_key)
     server_key = Base.encode64(hashed_key)
 
-    conn
-    |> resp(101, "")
-    |> put_resp_header("upgrade", "websocket")
-    |> put_resp_header("connection", "Upgrade")
-    |> put_resp_header("sec-websocket-accept", server_key)
-    |> put_websocket_extension_header(extensions)
-    |> send_resp()
+    headers =
+      [
+        {:upgrade, "websocket"},
+        {:connection, "Upgrade"},
+        {:"sec-websocket-accept", server_key}
+      ] ++
+        websocket_extension_header(extensions)
+
+    inform(conn, 101, headers)
   end
 
-  @spec put_websocket_extension_header(Plug.Conn.t(), extensions()) :: Plug.Conn.t()
-  defp put_websocket_extension_header(conn, []), do: conn
+  @spec websocket_extension_header(extensions()) :: keyword()
+  defp websocket_extension_header([]), do: []
 
-  defp put_websocket_extension_header(conn, extensions) do
+  defp websocket_extension_header(extensions) do
     extensions =
       extensions
       |> Enum.map_join(",", fn {extension, params} ->
@@ -97,6 +99,6 @@ defmodule Bandit.WebSocket.Handshake do
         |> Enum.join(";")
       end)
 
-    put_resp_header(conn, "sec-websocket-extensions", extensions)
+    [{:"sec-websocket-extensions", extensions}]
   end
 end

test/bandit/http1/request_test.exs

@@ -1809,7 +1809,7 @@ defmodule HTTP1RequestTest do
   end
 
   def send_inform(conn) do
-    conn = conn |> inform(100, [{"x-from", "inform"}])
+    conn = conn |> inform(100, [{:"x-from", "inform"}])
     conn |> send_resp(200, "Informer")
   end
 

test/bandit/http2/plug_test.exs

@@ -699,7 +699,7 @@ defmodule HTTP2PlugTest do
   end
 
   def send_inform(conn) do
-    conn = conn |> inform(100, [{"x-from", "inform"}])
+    conn = conn |> inform(100, [{:"x-from", "inform"}])
     conn |> send_resp(200, "Informer")
   end
 

test/bandit/websocket/http1_handshake_test.exs

@@ -33,6 +33,25 @@ defmodule WebSocketHTTP1HandshakeTest do
       assert Keyword.get(headers, :"sec-websocket-accept") == "s3pPLMBiTxaQ9kYGzzhZRbK+xOo="
     end
 
+    test "does not set content-encoding headers", context do
+      client = SimpleHTTP1Client.tcp_client(context)
+
+      SimpleHTTP1Client.send(client, "GET", "/", [
+        "Host: server.example.com",
+        "Accept-Encoding: deflate",
+        "Upgrade: WeBsOcKeT",
+        "Connection: UpGrAdE",
+        "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==",
+        "Sec-WebSocket-Version: 13"
+      ])
+
+      assert {:ok, "101 Switching Protocols", headers, <<>>} =
+               SimpleHTTP1Client.recv_reply(client)
+
+      assert Keyword.get(headers, :"content-encoding") == nil
+      assert Keyword.get(headers, :vary) == nil
+    end
+
     test "negotiates permessage-deflate if so configured", context do
       client = SimpleWebSocketClient.tcp_client(context)
 

test/bandit/websocket/upgrade_test.exs

@@ -50,6 +50,21 @@ defmodule WebSocketUpgradeTest do
       assert_in_delta now, then + 250, 50
     end
 
+    test "upgrade responses do not include content-encoding headers", context do
+      client = SimpleWebSocketClient.tcp_client(context)
+      SimpleWebSocketClient.http1_handshake(client, UpgradeWebSock, timeout: "250")
+
+      SimpleWebSocketClient.send_text_frame(client, "")
+      {:ok, result} = SimpleWebSocketClient.recv_text_frame(client)
+      assert result == inspect([:upgrade, :init])
+
+      # Ensure that the passed timeout was recognized
+      then = System.monotonic_time(:millisecond)
+      assert_receive :timeout, 500
+      now = System.monotonic_time(:millisecond)
+      assert_in_delta now, then + 250, 50
+    end
+
     defmodule MyNoopWebSock do
       use NoopWebSock
     end
@@ -69,10 +84,7 @@ defmodule WebSocketUpgradeTest do
                 %{
                   monotonic_time: integer(),
                   duration: integer(),
-                  req_header_end_time: integer(),
-                  resp_body_bytes: 0,
-                  resp_start_time: integer(),
-                  resp_end_time: integer()
+                  req_header_end_time: integer()
                 },
                 %{
                   connection_telemetry_span_context: reference(),

test/support/simple_websocket_client.ex

@@ -24,13 +24,11 @@ defmodule SimpleWebSocketClient do
     )
 
     # Because we don't want to consume any more than our headers, we can't use SimpleHTTP1Client
-    {:ok, response} = Transport.recv(client, 239)
+    {:ok, response} = Transport.recv(client, 164)
 
     [
       "HTTP/1.1 101 Switching Protocols",
       "date: " <> _date,
-      "vary: accept-encoding",
-      "cache-control: max-age=0, private, must-revalidate",
       "upgrade: websocket",
       "connection: Upgrade",
       "sec-websocket-accept: s3pPLMBiTxaQ9kYGzzhZRbK\+xOo=",